Digital audio data is transmitted over networks in many different settings. Telephone systems digitize voice and transmit digital voice data over telephone lines or cellular networks. Online service providers on the Internet can download audio files to computer users via conventional telephone or cable lines. Audio files can also be exchanged over traditional data networks, such as LANs (local area networks) and WANs (wide area networks), in a manner akin to electronic mail.
Current implementations of audio file transmission systems involve a transmission scheme in which the audio frames carrying the digital data are a fixed size. Present day modems operate at 9.6 kbps (kilobits per second), 14.4 kbps, and 28.8 kbps. The audio frames from an audio file are compressed at a bit rate for transmission over these various speed communication links. To ensure that transmission is possible over all three conventional speeds, the audio files are typically compressed at a bit rate of 8000 bits/second which can be sent to modems connected at 9.6 kbps, 14.4 kbps, and 28.8 kbps. While this rate will use most of the bandwidth available at 9.6 kbps, it uses only a fraction of the available bandwidth at 14.4 kbps and 28.8 kbps. Since the file is compressed at a lower quality rate of 8000 bits/second, the eventual reconstructed file has an equally low and fixed quality. The customers who use higher performing modems are penalized because they are unable to retrieve audio files of a quality commensurate with the performance of their systems.
It is therefore an aspect of this invention to provide an audio data transmission system which is scaleable to the communication link to use the maximum available bandwidth. In this way, a higher quality audio transmission can be provided to better performing modems.
In the online services setting, conventional systems require transmission of the entire audio file (whether compressed or uncompressed) before the recipient is able to play back the audio file. The audio file is at one fixed quality, such as that provided by the minimal compression rate of 8000 bits/second. For larger audio files carried over limited bandwidth channels (such as low-bandwidth telephone lines), the time required to download the whole audio file can take several minutes. This transmission delay is inconvenient to the recipient, particularly if the recipient is only browsing various audio files with little intent of listening to the entire audio file. The recipient is forced to request an audio file, await the slow transmission of the whole audio file at the minimal fixed bit rate, and then play it back.
Accordingly, it is another aspect of this invention to provide an optimal quality audio streaming in which the recipient can play the audio file as it is received.